1. Field of the Invention
The invention relates to a method of producing a dispersion liquid of a gelatinous electrolyte.
2. Description of Related Art
A fuel cell is a power generation system which obtains electric power by electrochemically reacting hydrogen and oxygen. In principle, the only product generated with power generation is water. Thus, the fuel cell draws attention as a clean power generation system which gives little load to the global environment. Depending on the kind of electrolytes, the fuel cell is classified into a solid polymer type, a phosphoric acid type, a molten carbonate type and a solid oxide type.
The solid polymer type fuel cell uses a proton-conductive ion-exchangeable solid polymer electrolyte membrane as an electrolyte. A membrane electrode assembly (MEA), which is a basic unit of the solid polymer type fuel cell, has a structure in which two sets of electrode catalyst layers are bonded to an upper surface and a lower surface of an ion-exchangeable solid polymer electrolyte membrane. In the case where the electrolyte used as a material of the ion-exchangeable solid polymer electrolyte membrane is a dispersion liquid of a gelatinous electrolyte, it is possible to manufacture the membrane electrode assembly without having to use an auxiliary material for bonding the electrode catalyst layers. For that reason, the gelatinous electrolyte is useful in manufacturing the solid polymer type fuel cell.
Japanese Patent Application Publication No. 2005-174587 (JP 2005-174587 A) discloses a gel electrolyte which is formed by mixing an acid and a polymer compound swelling against the acid. JP 2005-174587 A describes that the polymer compound is partially-methylated polybenzimidazole in which at least a part of substituents R of a specific polybenzimidazole structure is composed of a methyl group.
PCT International Publication No. WO 2013/031060 discloses a method of producing a catalyst ink used in forming a catalyst electrode, which includes a process of generating a catalyst dispersion liquid by dispersing catalyst-supporting particles, which are catalyst-supporting conductive particles, in a solvent, a process of preparing a gel body by mixing an ionomer and a volatile solvent, and a process of preparing a catalyst ink by stirring and mixing the catalyst dispersion liquid and the gel body. The ionomer is an ion-conductive polymer which is also used as a material of an electrolyte membrane. PCT International Publication No. WO 2013/031060 describes that perfluorosulfonic acid polymer such as Nafion (registered trademark) or the like may be used as the ionomer. Furthermore, PCT International Publication No. WO 2013/031060 describes that the ionomer used in the process of preparing the gel body by mixing the ionomer and the volatile solvent may preferably have an ion exchange equivalent weight (EW) value of 500 to 900 g/mol, the weight ratio of alcohol in a mixed solution may preferably be 5 to 20% by weight, and the heating temperature may preferably be in a range of 60 to 90° C.
Japanese Patent Application Publication No. 2010-129409 (JP 2010-129409 A) discloses a fuel cell including an electromotive part provided with a membrane electrode assembly which includes a fuel electrode, an air electrode and an electrolyte membrane sandwiched between the fuel electrode and the air electrode so as to make contact with a catalyst layer of the fuel electrode and a catalyst layer of the air electrode, wherein a gas diffusion layer of the fuel electrode includes a conductive porous base material filled with hydrophilic conductive particles having hydrophilicity. JP 2010-129409 A describes that the electrolyte membrane is composed of a proton-conductive material. Furthermore, JP 2010-129409 A describes that, since it is important that the water supplied from the air electrode through the electrolyte membrane is held by the fuel electrode, the respective members including the electrolyte membrane is hydrophilized by an acid treatment or the like.
PCT International Publication No. WO 2011/083842 discloses a method of producing a polymer electrolyte solution, which includes a pre-solution preparation process of preparing a pre-solution in which a polymer electrolyte having a side chain with a hydrophilic functional group is dissolved in a solvent, and a solution preparation process of obtaining a polymer electrolyte solution from the pre-solution by reducing at least water to a concentration of 10% or less. PCT International Publication No. WO 2011/083842 describes that the removal of water may be performed in a water bath. Furthermore, PCT International Publication No. WO 2011/083842 describes that at least one of a secondary alcohol and a tertiary alcohol may be used as the solvent.
As described above, different means have been developed with a view to providing a gelatinous electrolyte used in manufacturing a solid polymer type fuel cell. However, in the techniques of, e.g., JP 2005-174587 A and PCT International Publication No. WO 2013/031060, a problem exists in that the electrolyte to be gelled is limited to an electrolyte having a specific structure and/or a specific physical property (e.g., an EW value). Furthermore, in the technique of PCT International Publication No. WO 2011/083842, the viscosity can be increased. However, a problem exists in that the gelation may not sufficiently proceed.